1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus built-in to a muffler for a diesel engine, in which the exhaust gas normally flows through a filter in one direction and flows through the filter in the reverse direction when a regeneration of the filter is required.
2. Description of the Related Art
Japanese Unexamined Patent Publication Nos. 61-223215 and 62-210212 disclose an exhaust gas purifying apparatus having a filter comprising a ceramic honeycomb filter element arranged in the exhaust passage of the diesel engine to trap particulates, such as unburned hydrocarbon components, contained in the exhaust gas to prevent pollution of the atmosphere.
The filter traps the particulates by deposition on the filter element therein, and thus the filter element becomes clogged after long use. Therefore, the filter must be regenerated cyclically. The above publications disclose an arrangement of a heating means which comprises an electric heater adjacent to the filter, wherein the heater is cyclically activated to burn combustible particulates deposited on the filter element, such as unburned hydrocarbon components, to thereby regenerate the filter. For the regeneration of the filter, it is considered advantageous to arrange the heater downstream of the filter in the direction of the normal flow of the exhaust gas, and to cause the air containing exhaust gas to flow in a reverse direction through the filter, so that the burning flame is propagated toward the normal inlet side of the filter at which the particulates are deposited. To cause the reverse flow, the above publications disclose an arrangement of bypass pipes bypassing the filter accommodating main pipe, and bypass control valves in the bypass pipes.
The problem of the above described exhaust gas purifying apparatus is the provision of bypass pipes in addition to the filter accommodating main pipe, since this provision means that the apparatus must be large, and the mounting of such a large apparatus to the vehicle is cumbersome.